I think everyone should read about what John Deere the company is doing. This is not just about tractors: Here is the link:
John Deere is making it illegal to work on your own tractor, and I hope it hurts their sales. If this farmer had changed his belt sensor on his own tractor, he could have been put in prison for five years or fined a half million dollars under the DMCA law.
If you think you have nothing to worry about because you aren't a farmer, consider that this same scheme is being used by a number of manufacturers. When you buy a car, do you ask the salesman if you are allowed to do work on it, and do you believe his answer? Who really owns that car or tractor after you buy it?